Any of several large, powerful, pelagic fishes of the genus Tetrapturus allied to the marlins and sailfishes.

Spearfish (SS-190) was laid down on 9 September 1937 by the Electric Boat Co., Groton, Conn.; launched on 29 October 1938; sponsored by Mrs. Lawrence Y. Spear; and commissioned on 17 July 1939, Lt. C. E. Tolman, Jr., in command.

Spearfish conducted sea trials off New London and then held her shakedown cruise in the Guantanamo Bay area from 21 August to 3 October. She was overhauled at the Portsmouth (N.H.) Navy Yard from 1 November 1939 to 2 February 1940. On 10 February, she set sail for the west coast. After training operations in the San Diego training area from 6 March to 1 April, the submarine sailed to Pearl Harbor.

Spearfish operated between Hawaii and the west coast until 23 October 1941 when she departed Pearl Harbor and headed for Manila. She conducted training operations there from 8 November until the outbreak of war on 8 December (7 December west longitude time), when she began her first war patrol. This mission took her into the South China Sea, near Saigon and Camranh Bay, French Indochina, and off Tarakan and Balikpapan, Borneo. On 20 December, Spearfish encountered a Japanese submarine and made a submerged attack. She fired four torpedoes but all missed the target. She put into Surabaja, Java, on 29 January 1942 for refitting.

On 7 February, she began her second war patrol. Spearfish patrolled in the Java and Flores seas and made unsuccessful torpedo attacks on two cruiser task forces. On 2 March, she put into Tjilatjap, Java, and took on board 12 members of the staff of the commander of the submarines of the Asiatic Fleet, for transportation to Australia. The patrol ended at Fremantle, Australia.

Her third war patrol, from 27 March to 20 May, took her to the Sulu Sea and the Lingayen Gulf. On 17 April, she sank an enemy cargo ship of approximately 4,000 tons; and, on the 25th, she sank Toba Maru, a 6,995-ton freighter. On the night of 3 May, the submarine slipped into Manila Bay and picked up 27 passengers from Corregidor to be evacuated to Fremantle. She was the last American submarine to visit that beleaguered fortress before it surrendered.

From 26 June to 17 August, she scouted the South China Sea for enemy shipping and, from 8 September to 11 November, searched the west coast of Luzon where she damaged two freighters.

Spearfish sailed from Brisbane on 2 December 1942 and patrolled in the New Britain-New Ireland area for over a month before entering Pearl Harbor on 25 January 1943. From Oahu, she was directed to Mare Island for a major overhaul which lasted from 3 February to 19 May.

Spearfish returned to Pearl Harbor on 26 May and began her seventh war patrol from there on 5 June. She cruised the Truk Island area, made a photographic reconnaissance of Eniwetok Atoll, and then patrolled in the vicinity of Marcus Island. After refitting at Midway from 1 to 25 August, Spearfish searched Japanese home waters south of Bungo Suido for shipping. On the night of 10 and 11 September, she made a submerged torpedo attack on a convoy of seven freighters escorted by one destroyer and two torpedo boats. The submarine fired torpedoes at four ships and damaged two. Spearfish was depth charged throughout the day but finally eluded the escorts. On the night of 17 and 18 September, she attacked another convoy of seven ships with their escorts, sinking two and damaging one. Upon concluding this patrol, the ship sailed to Pearl Harbor for refitting.

From 7 November to 19 December, Spearfish performed photographic reconnaissance of Jaluit, Wotje, and Kwajalein, Marshall Islands, to aid the forthcoming invasion of those islands. On 5 and 6 December, she acted as lifeguard submarine for air strikes on Kwajalein and Wotje.

Spearfish's 10th war patrol was made south of Formosa from 17 January to 29 February 1944. On 30 January, she made two torpedo attacks on a convoy of three merchantmen and two escorts. She sank an escort and the passenger-cargo ship, Tomashima Maru. On 10 February, her attack on a convoy of four ships and their escorts damaged a freighter and sank a transport. The next day, she damaged another freighter in an 11-ship convoy. On the 12th, she crippled another freighter.

Spearfish sailed from Pearl Harbor on 31 March for the East China Sea and the area north of Nansei Shoto. On 5 May, she sank a freighter; and, the following day, she sank the cargo ship, Toyoura Maru. When the submarine returned to Pearl Harbor on 27 May, she was routed to the west coast for a major overhaul. After spending the period from 6 June to 3 October at the Mare Island Navy Yard, the ship returned to Pearl Harbor on 10 October and held training exercises for a month.

Spearfish's last war patrol took place from 12 November 1944 to 24 January 1945. On the first part of the patrol, she made photographic reconnaissance surveys of Iwo Jima and of Minami Jima. The submarine spent the second part in the Nanpo Shoto area on lifeguard duties and offensive patrols. On 19 December 1944, she rescued seven survivors of a crashed B-29. On 11 January 1945, her guns sank a sampan. She took three Japanese on board as prisoners, but one died several days later.

When she returned to Pearl Harbor on 24 January, Spearfish was used as a training ship until 18 August. On the 19th, she got underway for the west coast and arrived at Mare Island on 27 August. On 7 September, a Board of Inspection and Survey recommended that she be decommissioned immediately and possibly scrapped. It was decided to retain her in an inactive status for experimental explosive tests. The tests were cancelled, and Spearfish was decommissioned at Mare Island on 22 June 1946. She was struck from the Navy list on 19 July 1946; sold to the Lerner Co., Oakland, Calif.; and scrapped in October 1947.